1. Field of Invention
The invention relates to a chain drive for link chains of mining conveyors or mining extraction machines, in particular for scraper chain conveyors, with a drive shaft and sprocket tooth bodies.
2. Description of the Prior Art
Chain drives are used in mining operations, especially in chain conveyors, in particular scraper chain conveyors, and for powering mining extraction machines, especially coal plows and the like.
Chain conveyors are continuous conveyors and are the preferred means of conveyance, especially in the hard coal mining industry. The material to be conveyed is in this case moved by carriers (scrapers), which are fastened to electric motor-driven endless chains, in a conveyor trough.
A scraper chain conveyor is mainly composed of a drive station, the channel line, a one-, two- or three-part chain with carriers, a return station with auxiliary drive, with a shifting unit and the anchoring stations. Scraper chain conveyors are operated with high-strength chains. To drive the chain belts (chains with scrapers), the drive torque is delivered from the motor via a shaft in the sprocket mounted on the shaft. The sprocket transfers the tangential force to the chain via an interlocking mechanism.
Depending on the drive power and gear ratio installed on the conveyor, a chain must be chosen which has the required tensile strength. Stronger chains have larger dimensions and a longer pitch. Consequently, they run on a larger pitch circle around the sprocket. It is therefore advantageous, on the same shaft of a machine frame, to have the option of fitting several different shapes of sprocket to each chain as appropriate.
For drives for mining conveyors, a small sprocket diameter is required for reasons of space, resulting in the use of six or seven teeth on the circumference of a sprocket. Within this pitch circle diameter, there is only limited space for installation of the shaft cross-section and the sprocket. The drive shaft in particular however is subjected to a heavy load due to torsion (drive) and bending (tensile force on chain) and therefore needs to have a cross-section which ensures a sufficiently high shaft strength. Similarly, the chain teeth on the sprocket are subjected to a heavy bending load due to the tensile forces exerted on the chain. Therefore, the load-bearing surface must have a sufficiently high strength.
For scraper chain conveyors for heavy mining use, especially those with multi-chain drives, the chain is mounted as a removable part on the shaft in order to allow a worn sprocket to be replaced. The sprocket has the necessary form-fitting contours to allow it to interlock with the chain permanently incorporated into its outer circumference. The sprocket may consist of two halves which are positioned and screwed info place as half-shells around the shaft. The advantage of this is that the sprockets can be changed with the shaft installed. A disadvantage is that the screwing into place of the sprocket halves requires very strong screws which must be tightened with heavy tools (torque amplifier).
In another known embodiment, the sprocket is composed of a ring body which is mounted on the shaft. In the event of disassembly, the whole shaft with its load and the chain resting upon it must be removed from the machine frame and a bearing must be disassembled at one end of the shaft. The chain rings with internal teeth for torque absorption are also very expensive.
Generally, it should be noted that the screw connection of the sprocket halves with each other and the sprocket on the shaft is problematic, especially for very strong mining chains with wire diameters of up to 60 mm and maximum tensile forces of 4,500 kN to 5,000 kN. The necessary screws require a large amount of space for installation and therefore a minimum width of the sprocket. This makes it difficult to deliver the required torque. The disassembly and reassembly of the sprockets requires the removal of the shaft and is time-consuming. The necessary interruptions to operations lead to a loss of conveyor function.
When used with powerful drives, the link chains are subjected to exceptionally high stresses. As a result, the sprockets, especially the interlocking components (chain teeth, chain recesses) of the sprocket, are subject to a high degree of wear, due to rubbing of the chain links on the interlocking components, meaning that regular replacement is required. In the prior art, replaceable teeth solutions are known. Here, the sprocket or a sprocket base body is equipped with replaceable interlocking components, especially the chain sprocket teeth or tooth bodies.
Such proposals are known from EP 0 505 019 B1, CH 456 259 A, as well as DE 44 03 108 B4. Comparable solutions are published in U.S. Pat. No. 4,308,019 A and U.S. Pat. No. 2,038,895 A.
What all these proposals have in common is that replaceable interlocking components, in the form of teeth or tooth pairs, or sprocket tooth bodies more generally, are attached to the circumference of the sprocket. In this respect, different forms of execution are known. The sprocket tooth bodies can be installed in seats around the circumference of the sprocket and screwed into place. The stability of the teeth to prevent them tipping over due to the tensile forces exerted by the chain is achieved by screws, which press down the base of the tooth onto the surface of the sprocket. The screw connection is aligned with the center of the sprocket and forms the lowest point of attachment to the material of the sprocket.
Furthermore, the sprocket tooth bodies can also be fastened by pressing of the teeth into recesses on the upper surface of the chain sprocket. They are fastened by screws or bolts parallel to the direction of the shaft. The stability of the teeth to prevent them tipping over due to the tensile forces exerted by the chain is achieved by applying the base of the tooth to the surface of the sprocket. Furthermore, the sprocket tooth bodies can also be fastened in place by lateral overlapping of the sprocket disc. They are fastened by screws or bolts parallel to the direction of the shaft. During operation, these are subjected to high shear stresses due to the tensile forces exerted by the chain.
In addition, from U.S. Pat. No. 485,141 A, a chain drive for a link chain is known from the domain of mining conveyors. The conveying system demonstrated has at least one sprocket tooth body, which is coupled to a drive shaft. In addition, the sprocket tooth bodies can be set into seats in the drive shaft.
Generally speaking, the known replaceable teeth solutions for single-chain drives of a lighter construction are usable. However, it has not been possible to implement such solutions for high-performance applications, especially not for scraper chain conveyors, and they are also not technologically suited for such uses.